The present invention relates generally to digital communication networks, and more specifically, to methods and systems for efficiently transporting Fibre Channel/FICON client data over a SONET/SDH network path.
SONET/SDH and optical fiber have emerged as significant technologies for building large scale, high speed, IP (Internet Protocol)-based networks. SONET, an acronym for Synchronous Optical Network, and SDH, an acronym for Synchronous Digital Hierarchy, are a set of related standards for synchronous data transmission over fiber optic networks. SONET/SDH is currently used in wide area networks (WAN) and metropolitan area networks (MAN). A SONET system consists of switches, multiplexers, and repeaters, all connected by fiber. The connection between a source and destination is called a path.
One network architecture for the network interconnection of computer devices is Fibre Channel, the core standard of which is described in ANSI (American National Standards Institute) X3.230-1994. Arising out of data storage requirements, Fibre Channel currently provides for bidirectional gigabits-per-second transport over communication networks in Fibre Channel frames that consist of standardized sets of bits used to carry data over the network system. Fibre Channel links are limited to no more than 10 kilometers. Similar to Fibre Channel is FICON, a proprietary I/O channel which was developed by IBM for the data storage requirements for main frame computers.
New standards and protocols have emerged to combine the advantages of the SONET/SDH and Fibre Channel/FICON technologies. For example, it is sometimes desirable to link two SANs (Storage Area Networks), which operate with Fibre Channel or FICON protocols, over a MAN (Metropolitan Area Network), or even a WAN (Wide Area Network), which typically operate under SONET or SDH standards. This extension of Fibre Channel/FICON from 100 kilometers to over several hundred, or even thousand, kilometers, is made by mapping Fibre Channel/FICON ports to a SONET/SDH path for transport across a SONET/SDH network. One way to perform this function is to encapsulate Fibre Channel/FICON client data frames into transparent Generic Framing Protocol (GFP-T) frames and then map the GFP-T frames into SONET/SDH frames for transport across the SONET/SDH network. In this manner two Fibre Channel/FICON ports can communicate with each other over a SONET/SDH network as though the intervening network links are part of a Fibre Channel/FICON network. The Fibre Channel/FICON ports remain “unaware” of the SONET/SDH transport path.
However, even though Fibre Channel and FICON equipment are very similar, there are some crucial differences. For example, Fibre Channel devices handle duplicate frames and out-of-order frames much more reliably than FICON devices which may lockup when duplicate or out-of-order frames are received. Such duplicate or out-of-order frames are created under various SONET protection mechanisms, such as Unidirectional Path Switch Ring (UPSR) and Bidirectional Lines Switch Ring (BLSR), mainly because the same Fibre Channel/FICON data is bridged between two links under SONET/SDH protection and when span lengths are different between active and standby paths.
Since FICON protocol has difficulty in handling duplicate and out-of-order frames, there is a need for some mechanism by which duplicate and out-of-order frames are blocked. The present invention provides for such a mechanism which operates effectively for FICON (and Fibre Channel) frames.